Water Diffusion Process Research Articles

Multi-component apparent diffusion coefficients in human brain.

The signal decay with increasing b-factor at fixed echo time from brain tissue in vivo has been measured using a line scan Stejskal-Tanner spin echo diffusion approach in eight healthy adult volunteers. The use of a 175 ms echo time and maximum gradient strengths of 10 mT/m allowed 64 b-factors to be sampled, ranging from 5 to 6000 s/ mm2, a maximum some three times larger than that typically used for diffusion imaging. The signal decay with b-factor over this extended range showed a decidedly non-exponential behavior well-suited to biexponential modeling. Statistical analyses of the fitted biexponential parameters from over 125 brain voxels (15 x 15 x 1 mm3 volume) per volunteer yielded a mean volume fraction of 0.74 which decayed with a typical apparent diffusion coefficient around 1.4 microm2/ms. The remaining fraction had an apparent diffusion coefficient of approximately 0.25 microm2/ms. Simple models which might explain the non-exponential behavior, such as intra- and extracellular water compartmentation with slow exchange, appear inadequate for a complete description. For typical diffusion imaging with b-factors below 2000 s/mm2, the standard model of monoexponential signal decay with b-factor, apparent diffusion coefficient values around 0.7 microm2/ms, and a sensitivity to diffusion gradient direction may appear appropriate. Over a more extended but readily accessible b-factor range, however, the complexity of brain signal decay with b-factor increases, offering a greater parametrization of the water diffusion process for tissue characterization.

Cathodic electrocoat composition

Coatings on glass fibres, used to reinforce polyepoxide matrices, were examined by Fourier transform infra-red spectroscopy and by their reaction with styrene oxide, aniline, and also water in the vapour phase which was followed calorimetrically and gravimetrically. The coatings comprised an adhesive (of the DGEBA epoxy prepolymer type) applied on its own or together with a coupling agent (γ aminopropyltriethoxysilane). In all tests, these fibres were compared with untreated fibres of a similar type. The results of the studies indicate that the combination of the two coatings forms a reactive mixture within themselves which may inhibit uniform coating of the glass. It is also shown that the coating products on the glass control the process of water diffusion.

Capillary penetration in fibrous matrices studied by dynamic spiral magnetic resonance imaging

The dynamic spiral nuclear magnetic resonance (NMR) imaging technique was used to investigate the water imbibition into cellulose fiber matrices. The advancing water boundary, water concentration distribution, and swelling degree within the fiber matrix samples were monitored as a function of time over the entire absorption process. A combined image that shows the time evolution of the absorbed water concentration distribution within the fiber matrix was synthesized from the dynamically acquired NMR image data set. The NMR imaging data clearly demonstrated that water imbibition into a fiber matrix consists of two different processes: water penetration into capillaries between fibers and water diffusion into the cellulose fibers. The advancing liquid front is primarily determined by the water capillary flow and can be quantitatively described by Washburn equation. The slower water diffusion process in fibers is mainly responsible for the fiber swelling. The time evolution of the absorbed water concentration distribution can be qualitatively interpreted in terms of steady capillary flow and concentration-gradient-driven diffusion into fibers with a constant permeability. The effects of pore morphology, tortuosity, and surface heterogeneity to the water absorption process are also discussed.

Environmental Ageing of Adhesively-Bonded Joints. I. Dielectric Studies

High and low frequency dielectric measurements are reported on adhesively bonded aluminum structures aged by exposure to moisture over an extended period of time. The changes observed are interpreted in terms of initially water diffusing into the adhesive layer and there is little evidence of changes occurring to the surface oxide layer. Differences in the form and rate of change of the dielectric signature reflect the effects of the pretreatment and matrix resin on the water diffusion process. A good correlation is observed between the time domain data and the increased dielectric permittivity resulting from ingress of moisture into the adhesive bond. The paper illustrates the use of high frequency dielectric measurements in non-destructively probing adhesive bonds and indicates the potential for in-situ applications.

Theoretical Analysis of Osmotic Agents in Peritoneal Dialysis. What Size is An Ideal Osmotic Agent?

In this article the difference between osmotic fluid flow (ultrafiltration) as driven by osmotic pressure and diffusion through thin leaky membranes is discussed. It is pointed out that water transport induced by osmosis is fundamentally different from the process of water diffusion. Applying modern hydrodynamic pore theory, the molar solute concentration and the solute concentration in grams per 100 mL, exerting the same initial transmembrane osmotic pressure as a 1% glucose solution, was investigated as a function of solute molecular weight (MW). It was then assumed, base on experimental data, that the major pathway responsible for the peritoneal osmotic barrier characteristics is represented by pores of radius approximately 47 A. With increasing solute radius, the osmotic reflection coefficient (sigma) and, hence, the osmotic efficiency per mole of solute will increase. However, simultaneously, the molar concentration per unit solute weight will decrease. The balance point between these two events apparently occurs at a solute MW of approximately 1 kDa. An additional advantage of using solutes of high MW as osmotic agents during peritoneal dialysis (PD), rather than increased osmotic efficiency per se, lies in the fact that large solutes, due to their low peritoneal diffusion capacity, will maintain a sustained rate of ultrafiltration (osmosis) over a prolonged period. To illustrate this, we have performed computer simulations of peritoneal fluid transport according to the three-pore model of peritoneal permselectivity. According to these simulations, 4% of an 800 Da polymer solution (+50 mmol/L above isotonicity) will produce the same cumulative amount of intraperitoneal fluid volume ultrafiltered (UF) during 360-400 minutes as 4% of a 2 kDa polymer solution (+20 mmol/L) or 6.5% of a 10 kDa polymer solution (+6.5 mmol/L) having the same electrolyte concentration as dialysis solutions conventionally used for PD. Similar cumulative UF volumes (during 400 minutes) can be obtained by a 2.5% glycerol (+272 mmol/L) or a 3.2% glucose-containing dialysis solution (+177 mmol/L) with conventional electrolyte composition.

Molecular design of polymer membranes using molecular simulation technique

Diffusion processes of methane, water, and ethanol in poly(dimethylsiloxane) (PDMS) and polyethylene (PE) were investigated by molecular dynamics simulation. Pure liquid water and ethanol were also simulated. Simulations of 5 nanoseconds were performed for PDMS and PE with penetrant species, methane. The diffusion of methane in the polymer matrices exhibits anomalous (non-Einstein) behavior for time scales of 1 nanosecond. The excess chemical potentials of the penetrants in PDMS and the pure liquids were calculated by the Widom method. The excluded volume map sampling (EVMS) method and the continuum configurational bias (CCB) method were used to increase efficiency of sampling. Permeation rates, which were calculated from diffusion coefficients and solubilities, were in reasonable agreement with experiments.

Molecular Simulation of Permeation of Small Penetrants through Membranes. 1. Diffusion Coefficients

Molecular dynamics simulations have been carried out in order to examine the mechanism of diffusion of small penetrants in amorphous polymer membranes. Diffusion processes of methane, water, and ethanol in poly(dimethylsiloxane) (PDMS) and in polyethylene (PE) were investigated. Pure liquid water and ethanol were also simulated. The insertion probabilities P(R) of hard-sphere atoms of radius R into the polymers and the liquids were calculated. The free volume fraction, P(0), of PDMS is large and the insertion probability of a finite size atom into PDMS is widely distributed compared with the other polymers and liquids. Simulations of 5 ns were performed for PDMS and in PE with a penetrant species, methane

Migration behaviour of petroleum-associated short-chain organic acids

In order to increase our understanding of the origin of the short-chain organic acids (SCA) found in oilfield waters, peoperties that influence the possible mechanisms for migration from source rock to reservoir have been examined. The preferential partition of SCA between a synthetic formation water, and a modified crude oil, has been measured and shows the dominance of water solubility. The flooding of a modified petroleum containing SCA through a water-saturated core of reservoir-type rock shows that the pore water has a great capacity for extracting the SCA from the migrating oil phase. These factors make long-distance transport of SCA (dissolved in oil) from source rock to reservoir improbable; also, focused water flow or diffusion processes are not considered realistic mechanisms for long distance transport. In situ sources of SCA are required, and hydrous pyrolysis of crude oil mixed with reservoir type minerals shows that significant amounts of SCA can be generated and that the emplaced petroleum could thus be the source of the SCA found in oilfield waters.

Acrylic resins reinforced with woven highly drawn linear polyethylene fibres. 2. Water sorption and clinical trials.

The results reported in this paper are part of a continuing study of the reinforcement of acrylic denture base resins with highly drawn linear polyethylene fibres. Water sorption is significantly reduced by incorporation of these fibres, even though the water diffusion processes as such remain broadly unaffected. Clinical trials are encouraging and the reinforced dentures have been well accepted by all the patients.

A study of the effect of absorbed water on the Tg of a poly(amideimide) using DMA and DSC

The absorption by and diffusion of water in a commercially available poly(amideimide), Torlon ® 4203, and the dependence of the glass transition temperature ( T g) of this polymer on the weight % absorbed water have been investigated. Diffusion studies indicated that the activation energy for the diffusion process of water in this poly(amideimide) was 44.2 kJ mol −1 and that the permeability index was 1.17 × 10 −5 m 2 s −1. The diffusion coefficient was found to increase from 1.79 × 10 −13 m 2 s −1 at 303 K to 8.94 × 10 −13 m 2 s −1 at 333 K. The T g of the polymer, as determined from dynamic mechanical analysis (DMA), was found to decrease monotonically from 568 to 477 K as the weight % absorbed water in the polymer was increased from 0% to 4.25%. Linear least-squares analysis of the data indicated that the relationship between T g and weight % absorbed water ( W %Aw) was given by T g = 576.4 - 22.0 W %AW ( r 2 = 0.990). T g studies using differential scanning calorimetry (DSC) indicated that the diffusion of water from the sample had a major effect on correlations between T g and % absorbed water. That is, at low heating rates absorbed water diffused from the sample before the sample was heated to the glass transition temperature and therefore the measured T g was similar to that for a dry sample. The effect of absorbed water on the dimensional stability of this polymer when heated rapidly to temperatures in the vicinity of the glass transition temperature is also discussed.

加熱乾燥を受けるコンクリートの水分逸散過程解析に関する研究

When concrete is dried at elevated temperatures, distribution of temperature and moisture in concrete is formed immediately. These gradients change at every moment. In this paper, a mathematical model was presented to describe the drying process of concrete heated at elevated temperatures. Furthermore, a series of tests was carried out in which concrete and mortar cylinders of two different water-cement ratios were heated up to 80, 110, 150, and 200℃. These results of tests were analyzed by means of the mathematical model. As a result, it is shown that it is possible to analyze the water diffusion process of concrete, which involved the gradient of temperature, by using the same parameters even if the test conditions are different.

In vivo tritium contamination effects on water exchange across the erythrocyte membranes: a nuclear magnetic resonance study

The effects produced by chronic in vivo tritium contamination on the process of water diffusion across the rat erythrocyte membranes were investigated using an NMR relaxation method. As the level of tritium intake increased, an inhibition of the water permeability was observed, reaching values of 40% for corresponding absorbed doses of about 100 mGy. The activation energy of the transport process was also significantly increased, suggesting that the mechanism of the water diffusion across the membrane had changed.

水晶振動子を利用した微小重量測定技術によるヘテロポリ酸触媒内の拡散係数の測定

A piezoelectric quartz crystal microbalance was used to measure the diffusion coefficient of water in 12-tungstophosphoric acid catalyst. The catalyst was coated on the electrode surface of the quartz resonator and the time course of weight change caused by sorption/desorption could be followed in the nanogram range by measuring the frequency change. It was found that the diffusion rate increased with concentration of water absorbed and the response curve was successfully analyzed by assuming a diffusion coefficient as a function of concentration. This concentration dependency indicates that the diffusion process of water in a heteropoly acid is affected by the interaction with active sites. Isotope replacement studies using the same detection method revealed that the concentration dependency of diffusion coefficient disappeared. The obtained values of diffusion coefficients showed the same order as that by the unsteady method and lay in a reasonable order of magnitude.

Dehydration mechanism of bound water in sepiolite

The bound water dehydration of sepiolite was studied by high temperature X-ray diffractometry, thermogravimetry under controlled water vapour pressure and kinetic analysis of TG curves. The results show that the uniform folding of sepiolite crystals occurs when about 50% of the bound water is lost, entrapping the rest in the crystals. Before the folding, the dehydration rate is controlled by the water separation process from the magnesium atoms at the edges of channels, while, after the folding the rate is determined by the water diffusion process in the folded channels. Kinetic evaluation of TG curves yields an activation energy of 94 kJ mol −1 for the Kuzuu sepiolite and 106 kJ mol −1 for the Eskisehir sepiolite before the folding. The energy increases to 176 kJ mol −1 for the Kuzuu and 170 kJ mol −1 for the Eskisehir after the folding. It has been confirmed that the two-step dehydration of bound water is caused by the following two factors: (1) the difference in the activation energy of dehydration between the water in the unfolded open channel and that in the folded one, and (2) the change in the rate determining process from the water separation process to the water diffusion one.

Characterization of a coating layer on glass fibre used as reinforcing material in a polyepoxide matrix by means of FTIR spectroscopy and vapour phase interaction studies with monofunctional model compounds

Abstract Coatings on glass fibres, used to reinforce polyepoxide matrices, were examined by Fourier transform infra-red spectroscopy and by their reaction with styrene oxide, aniline, and also water in the vapour phase which was followed calorimetrically and gravimetrically. The coatings comprised an adhesive (of the DGEBA epoxy prepolymer type) applied on its own or together with a coupling agent (γ aminopropyltriethoxysilane). In all tests, these fibres were compared with untreated fibres of a similar type. The results of the studies indicate that the combination of the two coatings forms a reactive mixture within themselves which may inhibit uniform coating of the glass. It is also shown that the coating products on the glass control the process of water diffusion.

Diffusion Processes of Warm Water Discharged in Stratified Environment

Diffusion Processes of Warm Water Discharged in Stratified Environment

Water effects in polyaniline: A new conduction process

We present n.m.r. and conductivity measurements on polyaniline, which show that upon applying water vapour pressure: (i) protons exchange between the polymer and an adsorbed water phase; (ii) conduction is favoured. The diffusion process of water in a pellet is investigated. Finally, we propose a conduction mechanism based upon electron hopping between localized states, assisted by proton exchange.

えい航水そうにおける流れの可視化試験用の新しいトレーサーの開発

A tracer was developed to visualize the diffusion process of the soiled water discharged from the bottom of a hopper dredger in a towing tank.Comparative tests on several candidate tracers were conducted to select a tracer most suitable for this kind of visualization tests within the restrictions imposed on the tests in towing tank. As the results, the mixture of microscopic particles and water was chosen, which was obtained by filtering a red-colored soil with 100 μm mesh and adjusted to the specific gravity of 1.05.By using this tracer, diffusion process of discharged soiled water, namely the flow of the discharged soild water along the ship hull and accelerated by the propeller into its race and widely diffused, was successfully visualized. This tracer was shown to be useful for visualizing the macroscopic turbulent flow around the stern part of ship models.

DRYING MECHANISM OF COATED FILM OF POLYMER SOLUTION

Drying of coated film of polyvinylalcohol (PVA) aqueous solution is studied theoretically and experimentally, focusing on the diffusion process of water and the volumetric shrinkage of film occurring by evaporation of water. The diffusion coefficients were measured over the whole range of concentration by three methods, and drying experiments of coated films using hot air were performed. Numerical solutions were obtained from a set of transport equations for water using the observed diffusion coefficients and were compared with the experimental results.

WATER SORPTION AND WATER VAPOR PERMEABILITY OF NYLON 4

Equilibrium water sorption on Nylon 4 and diffusion process of water in the polymer were studied. Water sorptive ability of Nylon 4 is lower than that of regenerated cellulose, higher than that of cotton and three times of that of Nylon 6. The temperature dependence of the sorption isotherm is not significant.Diffusion coefficient obtained from the permeation experiment depends remarkably on the water content, which is common for the lyophilic polymers. In the case of water content 0.19g/g, Arrhenius_??_ plot of diffusion coefficients has an inflection at about 26°C, which is lower than the glass transition temperature. Sorption rate curve is not of Fickian type even at temperatures higher than the glass transition determined by dilatometry.